A variety of restraint systems have been devised to improve passenger safety in response to the increasing speed and congestion of vehicular traffic. In order to reduce injuries due to sudden accelerations produced in collisions, the most commonly employed systems have belts or harnesses to fasten about passengers as well as air bags which deploy when sensors determine a collision is beginning. These systems have been fairly effective in controlling passenger motion and absorbing the passengers' kinetic energy.
However, the performance of restraint systems has been put under new constraints due to recent changes in regulations for passenger safety in automobiles and aircraft. These regulations set standards for passenger protection.
For automobiles, the primary change has been a requirement that both upper and lower body safety be achieved by purely "passive" restraint systems. In this context, "passive" refers to the requirement that the passenger not have any active participation in the deployment or application of the restraint system once the passenger is seated in the vehicle. This is currently achieved by using automatically applied seat belts, airbags and knee bolsters. The most common configuration is an airbag to protect the upper torso and head and a knee bolster to provide lower torso restraint.
Thus there is a need for a passive restraint system, particularly one which more effectively controls and restrains a passenger's lower body.
In aircraft, there are new regulations governing the injury levels that passengers may experience in particular instances of sudden accelerations. The use of airbags and shoulder belts to control head excursion in multi-passenger aircraft is impractical.
Additionally, due to advantages in reduced cost and complexity, as well as a greater flexibility in interior layout, it is preferable that an aircraft passenger restraint system not require external power sources or complex sensor control systems.